IDENTIFICATION OF A NEUREGULIN AND PROTEIN-TYROSINE-PHOSPHATASE RESPONSE ELEMENT IN THE NICOTINIC ACETYLCHOLINE-RECEPTOR EPSILON-SUBUNIT GENE - REGULATORY ROLE OF AN ETS TRANSCRIPTION FACTOR

At the neuromuscular synapse, innervation induces endplate-specific ex pression of adult-type nicotinic acetylcholine receptors by selective expression of their subunit-encoding genes (alpha(2) beta epsilon delt a) in endplate-associated myonuclei. These genes are specifically regu lated by protein-tyrosine phosphatase (PTPase) activity, In addition, neuregulin/acetylcholine receptor-inducing activity, a nerve-derived f actor that stimulates nicotinic acetylcholine receptor synthesis, indu ces adult-type specific epsilon subunit gene expression via activation of a Ras/mitogen-activated protein kinase pathway, However, the DNA r egulatory elements and the binding proteins that mediate PTPase and ne uregulin-dependent gene expression remain unknown, Herein we report th at PTPase, neuregulin, and Ras-dependent regulation of the epsilon sub unit gene map to a 15-bp promoter sequence. Interestingly, this same 1 5-bp sequence appears to be necessary for low epsilon subunit gene exp ression in extrajunctional regions of the muscle fiber, Site-directed mutagenesis of a putative Ets binding site located within this 15-bp s equence, reduced PTPase, neuregulin, and Ras-dependent regulation. Ove rexpression of the rat muscle Ets-2 transcription factor resulted in a sequence-specific induction of epsilon subunit promoter activity, Fur ther, a dominant negative mutant of Ets-2 abolished neuregulin-depende nt induction of epsilon subunit gene expression, Thus, these results i ndicate a crucial role for the 15-bp element in determining synapse-sp ecific and neuregulin-mediated motor neuron control of epsilon subunit gene expression and suggest the participation of Ets transcription fa ctor(s) in this control.